Page 169 of the Goodheart-Willcox automotive encyclopedia, The Goodhean-Willcox Company, Inc., South Holland, Ill., 1995 describes that as fuel is burned in an internal combustion engine, about one-third of the heat energy in the fuel is convened to power. Another third goes out the exhaust pipe unused, and the remaining third must be handled by a cooling system. This third is often underestimated and even less understood.
Most internal combustion engines employ a pressurized cooling system to dissipate the heat energy generated by the combustion process. The cooling system circulates water or liquid coolant through a water jacket which surrounds certain pans of the engine (e.g., block, cylinder, cylinder head, pistons). The heat energy is transferred from the engine pans to the coolant in the water jacket. In hot ambient air temperature environments, or when the engine is working hard, the transferred heat energy will be so great that it will cause the liquid coolant to boil (i.e., vaporize) and destroy the cooling system. To prevent this from happening, the hot coolant is circulated through a radiator well before it reaches its boiling point. The radiator dissipates enough of the heat energy to the surrounding air to maintain the coolant in the liquid state.
In cold ambient air temperature environments, especially below zero degrees Fahrenheit, or when a cold engine is started, the coolant rarely becomes hot enough to boil. Thus, the coolant does not need to flow through the radiator. Nor is it desirable to dissipate the heat energy in the coolant in such environments since internal combustion engines operate most efficiently and pollute the least when they are running relatively hot. A cold running engine will have significantly greater sliding friction between the pistons and respective cylinder walls than a hot running engine because oil viscosity decreases with temperature. A cold running engine will also have less complete combustion in the engine combustion chamber and will build up sludge more rapidly than a hot running engine. In an attempt to increase the combustion when the engine is cold, a richer fuel is provided. All of these factors lower fuel economy and increase levels of hydrocarbon exhaust emissions.
To avoid running the coolant through the radiator, coolant systems employ a thermostat. The thermostat operates as a one-way valve, blocking or allowing flow to the radiator. FIGS. 40-42 (described below) and FIG. 2 of U.S. Pat. No. 4,545,333 show typical prior an thermostat controlled coolant systems. Most prior art coolant systems employ wax pellet type or bimetallic coil type thermostats. These thermostats are self-contained devices which open and close according to precalibrated temperature values.
Coolant systems must perform a plurality of functions, in addition to cooling the engine pans. In cold weather, the cooling system must deliver hot coolant to heat exchangers associated with the heating and defrosting system so that the heater and defroster can deliver warm air to the passenger compartment and windows. The coolant system must also deliver hot coolant to the intake manifold to heat incoming air destined for combustion, especially in cold ambient air temperature environments, or when a cold engine is started. Ideally, the coolant system should also reduce its volume and speed of flow when the engine parts are cold so as to allow the engine to reach an optimum hot operating temperature. Since one or both of the intake manifold and heater need hot coolant in cold ambient air temperatures and/or during engine start-up, it is not practical to completely shut off the coolant flow through the engine block.
Practical design constraints limit the ability of the coolant system to adapt to a wide range of operating environments. For example, the heat removing capacity is limited by the size of the radiator and the volume and speed of coolant flow. The state of the self-contained prior art wax pellet type or bimetallic coil type thermostats is typically controlled only by coolant temperature.
Numerous proposals have been set forth in the prior art to more carefully tailor the coolant system to the needs of the vehicle and to improve upon the relatively inflexible prior art thermostats.
U.S. Pat. No. 4,484,541 discloses a vacuum operated diaphragm type flow control valve which replaces a prior art thermostat valve in an engine cooling system. When the coolant temperature is in a predetermined range, the state of the diaphragm valve is controlled in response to the intake manifold vacuum. This allows the engine coolant system to respond more closely to the actual load on the engine. U.S. Pat. No. 4,484,541 also discloses in FIG. 4 a system for blocking all coolant flow through a bypass passage when the diaphragm valve allows coolant flow into the radiator. In this manner, all of the coolant circulates through the radiator (i.e., none is diverted through the bypass passage), thereby shortening the cooling time.
U.S. Pat. No. 4,399,775 discloses a vacuum operated diaphragm valve for opening and closing a bypass for bypassing a wax pellet type thermostat valve. During light engine load operation, the diaphragm valve closes the bypass so that coolant flow to the radiator is controlled by the wax pellet type thermostat. During heavy engine load operation, the diaphragm valve opens the bypass, thereby removing the thermostat from the coolant flow path. Bypassing the thermostat increases the volume of cooling water flowing to the radiator, thereby increasing the thermal efficiency of the engine.
U.S. Pat. No. 4,399,776 discloses a solenoid actuated flow control valve for preventing coolant from circulating in the engine body in cold engine operation, thereby accelerating engine warm-up. This patent also employs a conventional thermostat valve.
U.S. Pat. No. 4,545,333 discloses a vacuum actuated diaphragm flow control valve for replacing a conventional thermostat valve. The flow control valve is computer controlled according to sensed engine parameters.
U.S. Pat. No. 4,369,738 discloses a radiator flow regulation valve and a block transfer flow regulation valve which replace the function of the prior an thermostat valve. Both of those valves receive electrical control signals from a controller. The valves may be either vacuum actuated diaphragm valves or may be directly actuated by linear motors, solenoids or the like. In one embodiment of the invention disclosed in this patent, the controller varies the opening amount of the radiator flow regulation valve in accordance with a block output fluid temperature.
U.S. Pat. No. 5,121,714 discloses a system for directing coolant into the engine in two different streams when the oil temperature is above a predetermined value. One stream flows through the cylinder head and the other stream flows through the cylinder block. When the oil temperature is below the predetermined value, a flow control valve closes off the stream through the cylinder block. Although this patent suggests that the flow control valve can be hydraulically actuated, no specific examples are disclosed. The flow control valve is connected to an electronic control unit (ECU). This patent describes that the ECU receives signals from an outside air temperature sensor, an intake air temperature sensor, an intake pipe vacuum pressure sensor, a vehicle velocity sensor, an engine rotation sensor and an oil temperature sensor. The ECU calculates the best operating conditions of the engine cooling system and sends control signals to the flow control valve and to other engine cooling system components.
U.S. Pat. No. 5,121,714 employs a typical prior an thermostat valve 108 for directing the cooling fluid through a radiator when its temperature is above a preselected value. This patent also describes that the thermostat valve can be replaced by an electrical-control valve, although no specific examples are disclosed.
U.S. Pat. No. 4,744,336 discloses a solenoid actuated piston type flow control valve for infinitely varying coolant flow into a servo controlled valve. The solenoids receive pulse signals from an electronic control unit (ECU). The ECU receives inputs from sensors measuring ambient temperature, engine input and output coolant temperature, combustion temperature, manifold pressure and heater temperature.
One prior art method for tailoring the cooling needs of an engine to the actual engine operating conditions is to selectively cool different portions of an engine block by directing coolant through different cooling jackets (i.e., multiple circuit cooling systems). Typically, one cooling jacket is associated with the engine cylinder head and another cooling jacket is associated with the cylinder block.
For example, U.S. Pat. No. 4,539,942 employs a single cooling fluid pump and a plurality of flow control valves to selectively direct the coolant through the respective portions of the engine block. U.S. Pat. No. 4,423,705 shows in FIGS. 4 and 5 a system which employs a single water pump and a flow divider valve for directing cooling water to head and block portions of the engine.
Other prior art systems employ two separate water pumps, one for each jacket. Examples of these systems are given in U.S. Pat. No. 4,423,705 (see FIG. 1), U.S. Pat. No. 4,726,324, U.S. Pat. No. 4,726,325 and U.S. Pat. No. 4,369,738.
Still other prior art systems employ a single water pump and single water jacket, and vary the flow rate of the coolant by varying the speed of the water pump.
U.S. Pat. No. 5,121,714 discloses a water pump which is driven by an oil hydraulic motor. The oil hydraulic motor is connected to an oil hydraulic pump which is driven by the engine through a clutch. An electronic control unit (ECU) varies the discharge volume of the water pump according to selected engine parameters.
U.S. Pat. No. 4,079,715 discloses an electromagnetic clutch for disengaging a water pump from its drive means during engine start-up or when the engine coolant temperature is below a predetermined level.
Published application nos. JP 55-35167 and JP 53-136144 (described in column 1, lines 30-62 of U.S. Pat. No. 4,423,705) disclose clutches associated with the driving mechanism of a water pump so that the pump can be stopped under cold engine operation or when the cooling water temperature is below a predetermined value.
The goal of all engine cooling systems is to maintain the internal engine temperature as close as possible to a predetermined optimum value. Since engine coolant temperature generally tracks internal engine temperature, the prior art approach to controlling internal engine temperature control is to control engine coolant temperature. Many problems arise from this approach. For example, sudden load increases on an engine may cause the internal engine temperature to significantly exceed the optimum value before the coolant temperature reflects this fact. If the thermostat is in the closed state just before the sudden load increase, the extra delay in opening will prolong the period of time in which the engine is unnecessarily overheated.
Another problem occurs during engine start-up or warm-up. During this period of time, the coolant temperature rises more rapidly than the internal engine temperature. Since the thermostat is actuated by coolant temperature, it often opens before the internal engine temperature has reached its optimum value, thereby causing coolant in the water jacket to prematurely cool the engine. Still other scenarios exist where the engine coolant temperature cannot be sufficiently regulated to cause the desired internal engine temperature.
When the internal engine temperature is not maintained at an optimum value, the engine oil will also not be at the optimum temperature. Engine oil life is largely dependent upon wear conditions. Engine oil life is significantly shortened if an engine is run either too cold or too hot. As noted above, a cold running engine will have less complete combustion in the engine combustion chamber and will build up sludge more rapidly than a hot running engine. The sludge contaminates the oil. A hot running engine will prematurely break down the oil. Thus, more frequent oil changes are needed when the internal engine temperature is not consistently maintained at its optimum value.
Prior art cooling systems also do not account for the fact that the optimum oil temperature varies with ambient air temperature. As the ambient air temperature declines, the internal engine components lose heat more rapidly to the environment and there is an increased cooling effect on the internal engine components from induction air. To counter these effects and thus maintain the internal engine components at the optimum operating temperature, the engine oil should be hotter in cold ambient air temperatures than in hot ambient air temperatures. Current prior art cooling systems cannot account for this difference because the cooling system is responsive only to coolant temperature.
Additionally, in order to control the flow of coolant between the cylinder head and the engine block, prior art cooling systems incorporated complicated valving arrangements which must be separately mounted to the engine and which occupy a significant amount of valuable engine compartment space. U.S. Pat. Nos. 4,539,942 and 5,121,714 illustrate typical cooling fluid control systems with complex valving arrangements.
Prior art cooling systems have also not taken full advantage of the heat generated during combustion of the air/fuel mixture. As discussed above, approximately one third of heat generated during the combustion of the fuel/air mixture is transferred through the exhaust system. Several prior art systems have attempted to utilize this heat for improving the efficiency of an engine. For example, U.S. Pat. No. 4,079,715 discloses a prior art method for using exhaust gases to heat the intake air. Special exhaust passageways are attached to the exhaust manifold and direct the exhaust gases through or adjacent to the intake manifold thereby permitting convection of the exhaust gas heat to the intake air.
A second prior art method for utilizing the heat in the exhaust gases is disclosed on pages 229 of the Goodheart-Willcox automotive encyclopedia, The Goodheart-Willcox Company, Inc., South Holland, Ill., 1995. This method requires the incorporation of a special duct or "crossover passage" around the exhaust manifold that traps the heat which is otherwise dissipated. This trapped heated air is then routed to the intake manifold where it preheats the intake air.
These prior art methods all require the addition of special, relatively heavy ducting which must be designed to be thermally compatible with the temperatures in the exhaust gases. Additionally, these systems have all been limited to heating the intake air. Hence, the prior art methods have not utilized the heat in the exhaust gases to assist in preheating the engine and/or the engine oil.
While many of the prior art systems address the problem of cooling an internal combustion engine, none have provided a workable, cost efficient system. Accordingly, a need therefore exists for a system which optimally controls the flow of a fluid in a cooling system and which requires minimal modifications to the current engine arrangement.